A new potential heart medicine, code-named X-281, is being tested by a pharmaceu

Question

A new potential heart medicine, code-named X-281, is being tested by a pharmaceutical company, Pharma-pill. As a research technician at Pharma-pill, you are told that X-281 is a monoprotic weak acid, but because of security concerns, the actual chemical formula must remain top secret. The company is interested in the drug's K_a value because only the dissociated form of the chemical is active in preventing cholesterol buildup in arteries. To find the pK_a of X-281, you prepare a 0.084 M test solution of X-281 at 25.0 degree C. The pH of the solution is determined to be 2.40. What is the pK_a of X-281? Express your answer numerically.

Explanation / Answer

PH = 1/2Pka -1/2logC

PH = 2.4

C = 0.084M

PH = 1/2Pka -1/2logC

2.4 = 1/2*PKa -1/2log0.084

2.4 = 1/2Pka -1/2*-1.0757

2.4 = 1/2Pka+0.53785

1/2Pka = 2.4-0.53785

1/2Pka   = 1.862

    Pka   = 1.862*2

   PKa = 3.724

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